Face type rotary mechanical seals are used extensively for high pressure dynamic shaft seals. Materials used for face seals include graphite or carbon. The sealing efficiency of these seals increases as the pressure differential across the seal increases; the greater the pressure, the better the seal. However, carbon face seals begin to fail at low pressures. They need a guaranteed minimum pressure to maintain a positive seal at a given shaft speed.
Other shaft sealing techniques include use of O-ring seals. O-ring seals are generally limited by excessive pressures and shaft speeds. They have a tendency to fail at high pressures and high shaft speeds. However, they are very reliable at low pressures and low shaft speeds.